Cyclic gas injection, also known as gas huff and puff, in a single-well EOR process that involves the injection of a slug of gas into a well. Although field results indicate that cyclic CO2 injection may be successfully implemented, application of CO2 are limited due to CO2 transportation costs and economic problems. This paper showcases the simulation study of the single-cycle gas injection using mixtures of methane, butane, and nitrogen to CO2. Cyclic gas injections were performed at both immiscible and miscible conditions to see whether the optimum mixtures that results in maximum oil recovery is different from two conditions. A compositional simulation model using detailed geologic characterization was built to optimize gas injection design. The model is radial model with production and injection well are on the center of the model. The Peng-Robinson Equation of State (EOS) was chosen to describe the phase behavior during the injection phase. Several compositions of gas mixture were run to find the optimum mixture and its portion to CO2 that gives the best cumulative oil production. Each composition of gas mixtures simulated in two soaking time to see its effect to the oil recovery. Gas injection mechanism that have been analyzed from this simulation are viscosity reduction, oil swelling, and increment of reservoir pressure. This study found that mixture of CO2 with methane and nitrogen can increase the amount of oil recovered compared to the pure CO2 if injected to reservoir using huff and puff method. Additional study in this paper found that pre-N2 injection in conventional single cycle CO2 huff and puff can increase amount of recovered oil in immiscible condition.